Generally, the battery pack of this type is attachable to and detachable from a grip part of an electric tool or a battery charger, and is so constructed that when the battery pack has been attached, positive and negative terminals of the battery pack are brought into contact with terminals provided on the object equipment such as the electric tool, the battery charger, and so on.
By the way, as disclosed in JP-A-2001-229895, there has been known a conventional attaching structure of the battery pack which is so constructed that a hook is provided in a rear part of the battery park, and locking means to be locked to and unlocked from a receiving part of the electric tool is linked to the hook. Attaching of the battery pack is performed by sliding the battery pack forward toward a determined position of the object equipment to push it in, and by locking the locking means to the receiving part of the object equipment. On the other hand, detaching of the battery pack can be performed by pushing the hook on the back face downward with fingers to release the locked state of the locking means, and thereafter, by withdrawing the battery pack backward.
Besides, as disclosed JP-A-2004-039638, there has been known another conventional attaching structure of a battery pack which is so constructed that a pair of operation parts are provided at both sides of the battery pack, and detaching of the battery pack can be performed by pressing the operation parts with a thumb and an index finger of a single hand so as to clamp them from below thereby to release the lock between the battery pack and the object equipment such as the electric tool.
However, in the structure as disclosed in JP-A-2001-229895, when the battery pack is removed, a direction of a force to be applied for releasing the lock of the hook (a downward direction) and a direction in which the battery pack is withdrawn (a backward direction) are different from each other, and it is difficult to apply appropriate amounts of the forces. Because the force in the downward direction for releasing the lock is still maintained after the lock has been released, there has been such a problem that the battery pack cannot be retained when it has been detached from the object equipment, and the battery pack may be dropped and broken.
Moreover, in the structure as disclosed in JP-A-2004-039638, recesses are formed in a vertical direction on both side faces of the battery pack below the operating parts, and the battery pack is withdrawn in a state where the thumb and the index finger are inserted into the recesses from below. Because the battery pack is horizontally withdrawn with the thumb and the index finger directed upward and downward, it has been impossible to use the forces efficiently. Moreover, there has been such a risk that the fingers may be disengaged from the recesses with the force for withdrawing, and the battery pack may be dropped. There has been a further problem that it is difficult to obtain sufficient strength against an impact at a time of dropping, because a large locking member cannot be provided in view of a space.